"All the ash and some of the contaminants that are coming off the landscape when we start to get those rains, is going to be washing those materials into the river, right above the city of Fort McMurray."

Silins, who is among several water scientists working with the Alberta government on a recovery plan for Fort McMurray, says the contaminated water will be difficult to treat.

Though rain would provide long-awaited relief to firefighters on the front line, it would be a double-edged sword for water treatment officials.

Spring showers can wash wildfire contaminants into the Athabasca River, which feeds Fort McMurray's water treatment plant. And each rainfall would wash a new wave of contaminants down the riverbanks.

Silins says roughly 30 km of the Athabasca River bank, and more than 100 km of the Clearwater River have been heavily contaminated so far.

"We have very limited experience with these kinds of large, severe wildfires, right on top of a community where you have a water treatment plant."

As of Wednesday evening there is a 70 per cent chance of showers in Fort McMurray for Thursday.

Fort McMurray well-equipped

After a wildfire, water quality can change quickly — and keeping a close watch on water quality and prevailing weather conditions will be critical in the weeks and months to come.

Fort McMurray's water treatment plant wasn't damaged by the fire, which continues to rage north and well east of the city. The entire Wood Buffalo area remains under a boil-water advisory.

Silins says the Fort McMurray treatment plant is well-equipped to handle the disaster. It relies on the same technology Calgary uses, which served that city well following the floods of 2013.

"That technology is pretty well-aligned to deal with rapidly changing water quality, which is one of the things we're concerned about.

"When the rains come, we'll see these contaminants coming off, but at higher levels than they're used to seeing. And as the rains come, we're going to see the quality change very rapidly, and that's the biggest challenge."

Watershed will be slow to recover

Thoughresearch is limited, Silins says the Lost Creek wildfire of 2003 provided scientists some clues about wildfire contamination in rivers.

According to his study on the southern Alberta fire, it could be years before the watershed fully recovers.

Nitrogen levels, for instance, will return to baseline after five to six years. However, other contaminants such as sediment, organic carbon, and a deluge of harmful nutrients will likely remain present in the headwaters of Fort McMurray more than a decade from now.

"As a consequence, we haven't seen some of the aquatic ecology recover at all after that Lost Creek fire," said Silins.

"The plants that are growing in the streams, the algae, the invertebrates, the insects that live in the stream ... and even fish that are making use of it. The entire eco-system responds."